1. Field of the Invention
The present invention relates to a method of growing a compound semiconductor, a compound semiconductor growth apparatus and a method of forming a compound semiconductor device, and more particularly to a method of forming a compound semiconductor epitaxially on a compound semiconductor single crystal substrate selectively, a compound semiconductor growth apparatus and a method of manufacturing a compound semiconductor device including the epitaxial growth process.
More, the present invention relates to a compound semiconductor device and a method of measuring a defect of a compound semiconductor layer.
2. Description of the Prior Art
New electronic devices and optical devices have been realized by forming an epitaxial growth layer on a single crystal semiconductor substrate and forming this epitaxial growth layer in multiple layers or in a heterostructure. In particular, a quantum effect device for confining electrons in a low dimensional structure to bring out a quantum effect of electrons and an electronic wave interference logic element utilizing the nature of an electron wave have been devised by combining microlithography and heteroepitaxial technology. They are called quantization function devices, and are expected to be put to practical use in the near future as a new electronic device.
As the epitaxial technology in these cases, a molecular beam epitaxy (MBE) or a metalorganic vapor phase epitaxy (MOVPE) etc. is known. These technologies are featured by a point that a super-thin film can be grown with high controllability.
In order to supply molecular beam source materials in the MBE, a structure that a metal source is held in a vacuum chamber (a crystal growth chamber) is adopted. Development of a gas source molecular beam epitaxy (GSMBE) adopting a gas introduction method in which a gaseous source containing a metalorganic compound is provided outside a vacuum chamber and the source is introduced into the vacuum chamber through a gas introduction valve has become active recently. The GSMBE is also referred to as Metalorganic MBE (MOMBE) or Chemical Beam Epitaxy (CBE).
MBE, MOVPE or GSMBE used as heteroepitaxial technology has features in a growth process on a semiconductor substrate, respectively. In particular, a fact that a mask for patterning is formed on a semiconductor substrate and a heteroepitaxial layer is grown on the substrate surface will be described as follows.
(1) MBE
Due to the fact that the growth principle of the MBE is close to physical vapor deposition, it is possible to grow a single crystal layer of GaAs or AlGaAs on a GaAs single crystal surface when a compound semiconductor layer is grown on a GaAs substrate for instance using a mask composed of SiN.sub.x applied with patterning. A pattern of a single crystal of GaAs or AlGaAs is formed at a part that is not covered with a mask.
On the other hand, a polycrystalline GaAs or AlGaAs layer is deposited on the SiN.sub.x film. The control of the thickness of the single crystal layer does not depend on the size and the configuration of a window of the mask, but is determined by the intensity of the molecular beam that reaches the mask or the surface of the single crystal layer. This is an advantageous point in the production of a microstructure.
Althouqh the polycrystalline layer formed on the mask can be utilized as an insulating layer, it becomes necessary to remove the polycrystalline layer by a lift-off method or the like when a heterostructure or an electrode is formed in an area by the single crystal layer pattern.
(2) MOVPE
In the MOVPE, features of selective growth on the substrate also undergo a change depending on the difference whether the gas pressure in a furnace during growth is a normal pressure or a reduced pressure.
In the case of normal pressure MOVPE, a polycrystalline or amorphous film is accumulated on an insulating film such as a SiN.sub.x film used as a mask. Further, a single crystal film is grown on a single crystal plane that is not covered with the mask. However, it is known that what is called an edge effect that a growth rate on a single crystal plane changes depending on an area ratio of an area where the insulating film is formed to an area where the single crystal layer is in existence, or the growth rate in an area near the insulating film in the single crystal plane is produced.
In the case of low-pressure MOVPE, while the polycrystalline or amorphous film becomes more difficult to be accumulated on the insulating film as the pressure is reduced, the change of the growth rate and the edge effect due to the area ratio of the insulating film (a mask) to the single crystal plane become conspicuous.
The edge effect is described in the following document.
1! Kenji HIRUMA et al., Journal of Crystal Growth 102, pp. 717-724, 1990
(3) GSMBE
In GSMBE, when GaAs is grown in a state that a mask composed of SiN.sub.x (an insulating film) applied with patterning is formed on the GaAs substrate for instance, nothing is accumulated on the mask, and neither the change of the growth rate nor the edge effect on the single crystal plane due to the area ratio of the insulating film to the single crystal plane is observed at all. This is originated in that the GSMBE is the growth by a surface reaction mechanism between the molecular beam material and the solid surface.
The virtue of selectivity of the growth by the GSMBE is very effective when a quantum functional device is produced by heteroepitaxial growth on the semiconductor substrate. Similarly to the case of the MBE, however, such a combination of the molecular beam material and the insulating film that a polycrystalline film or an amorphous film is accumulated on an insulating film is in existence.
For example, when an AlGaAs single crystal is grown selectively using a patterning mask composed of SiN.sub.x, an AlGaAs polycrystalline or amorphous film is accumulated on the mask. This is because of such a reason that the metalorganic is very active and decomposition reaction is also generated even on the SiN.sub.x film and the insulating film. The AlGaAs single crystal layer or the single crystal layer having Al in the composition thereof is a very important layer in producing an electronic device of a GaAs system, and the demand for technical development for growing these layers selectively is great.
In the following document, it is disclosed that an AlGaAs layer can be grown selectively without accumulating a polycrystalline or amorphous film on a SiN.sub.x patterning mask film by adding hydrogen chloride gas (Hc1) during growth of AlGaAs by MOVPE.
2! Kenji Shimoyama, Katsuji Fujii, Yuichi Inoue and Hideki Goto, Institute of Applied Physics, Applied Electronic Physical Properties Subcommittee Meeting Research Paper (AP922227), No. 445, pp. 15-20, 1992
As a model of the duty of (Hc1) gas on the improvement of selectivity, it is considered that dangling bond on the SiN.sub.x film surface is terminated with Cl and the reaction between a growth species containing Al and the SiN.sub.x film is reduced.
Even when a method of adding (Hc1) gas during growth by MOVPE is adopted, it is impossible to completely eliminate the area ratio effect of the pattern and the edge effect described previously, and controllability of the growth rate is low in forming a pattern of a microstructure. With the area ratio effect, such a problem that it becomes more difficult to obtain an even device characteristic in one semiconductor integrated circuit is presented. Further, since the semiconductor layer is curved according to the edge effect, there are such problems that carrier travelling performance of the electronic device is deteriorated, optical confinement of an optical device becomes poorer and so on.
Further, since (Hc1) gas acts as etching gas of GaAs or AlGaAs, the growth rate of the semiconductor becomes more difficult to be controlled by the addition of (Hc1), and an even device characteristic is difficult to obtain when an electronic device or an optical device is formed.